A known image forming apparatus is provided with photosensitive members, which are horizontally arranged in tandem, in correspondence with yellow, magenta, cyan and black toner. Such a tandem image forming apparatus can print in color at substantially the same speed as printing in monochrome, because a toner image of each color is formed at substantially the same time on each corresponding one of the photosensitive members and each of the different colored images is sequentially laid on top of a sheet while the sheet passes through the photosensitive members.
As disclosed in, for example, Japanese Laid-Open Patent Publication No. 2003-15378, a tandem image forming apparatus is proposed that includes a frame for integrally supporting photosensitive members, each associated with one color. The frame is slidably installed in or removed from a main body of the image forming apparatus. A developing cartridge for developing an electrostatic latent image formed on each of the photosensitive members is removably set in the frame.
In the image forming apparatus disclosed in the Japanese Laid-Open Patent Publication No. 2003-15378 or its counterpart U.S. Pat. No. 6,708,011, a plate-like guide projection is formed on each side of the developing cartridge so as to extend vertically. A guide groove for receiving the guide projection is formed on an upper inner portion of each side plate of the frame at a position corresponding to each photosensitive member. The guide projections are inserted into the guide grooves from above, to set the developing cartridge in the frame or remove the developing cartridge from the frame along the guide grooves.
A developing roller shaft is disposed below the guide projection on each side of the developing cartridge having the guide projection formed thereon. When force is input to the developing roller shaft to rotate the shaft, stress is applied to the guide projection in its thickness direction, so that the guide projection may be broken.